Update go.mod and vendor

vendor/github.com/moby/buildkit/util/system/path_unix.go

@@ -1,14 +0,0 @@
-// +build !windows
-
-package system
-
-// DefaultPathEnv is unix style list of directories to search for
-// executables. Each directory is separated from the next by a colon
-// ':' character .
-const DefaultPathEnv = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
-
-// CheckSystemDriveAndRemoveDriveLetter verifies that a path, if it includes a drive letter,
-// is the system drive. This is a no-op on Linux.
-func CheckSystemDriveAndRemoveDriveLetter(path string) (string, error) {
-	return path, nil
-}